ASTM D4924-21

4.1Petroleum waxes in rubber compounds are commonly used to provide protection from degradation by ozone under static conditions, that is, when there is little or no flexing of the rubber products. The mode of action for this protection is (4.2This standard classifies the petroleum waxes on the basis of molecular weight. In general, waxes of lower molecular weight (paraffinic or crystalline) migrate through the rubber more rapidly and form more brittle film than the higher molecular weight waxes (microcrystalline). Wax mixtures and blends are commonly used.

4.3No direct inference of suitability for use in a particular rubber compound is made or implied by the classifications herein.

1.1This classification is intended to establish a classification system and test methods for petroleum waxes used in rubber compounding primarily as a static protective agent or material for unsaturated rubbers such as styrene-butadiene rubber, polyisoprene rubber, natural rubber, chloroprene rubber, acrylonitrile-butadiene rubber, and polybutadiene rubber. These unsaturated rubbers are subject to ozone cracking. Under certain exposure conditions, waxes retard this cracking.

1.2This classification is applicable to petroleum waxes used as process aids in rubber compounding. It is not applicable to nonpetroleum waxes such as carnuba wax, candelille wax, or ceresin wax, nor to synthetic hydrocarbon waxes such as polyethylene wax. These non-petroleum waxes display a different behavior on gas chromatographic analysis than do petroleum waxes.

1.3This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.